This invention relates to a carburetor for Otto cycle motors, of the type wherein the fuel is kept at a constant level within a fuel chamber and is introduced in the air flow, sucked by the motor, by the effect of depression produced by the flow in the nozzle throat area of a venturi tube choke.
In the known carburetors with a single body, the control of the motor speed is effected by means of a throttle valve which reduces in a variable ratio the intake pipe downstream from the choke. In the greatest part of the operating conditions, the resulting flow is therefore throttled and its speed through the choke is not the optimum one which produces the best admixture conditions. For said reasons, and due to the fact that the jet nozzle is unchangeable, it is not possible to obtain for all the operating conditions the most rational fuel feeding, and compromises must be accepted whose results are efficiency losses, worsening of the combustion and a greater atmospheric pollution.
An improvement of said conditions is obtained by the twin carburetors, wherein a first carburetor body controls the motor operation within the range of lower speed, in which a second body remains inactive, while from a preestablished condition onwards the first body continues its operation without any throttle, and the control is entrusted to the second body, which acts in parallel with the first one. Also in this case, however, there is a great number of operating conditions wherein an important fraction of the fuel is introduced in a highly throttled choke and causes efficiency losses, a bad combustion and pollution.